US2371416A - Reception of timing modulated waves - Google Patents

Description

March 13, 1945. H. TUNlcK l -RECEPTION OF TIMING MODULATED WAVES l original Filed Dec.- 2o, 1941 3 Sheets-Sheet 1 .Ummm O Imzmzou H. TuNlcK 2,371,416

RECEPTION OF TIMING kMODULTED WAVES 3 SheetsfSheet 2 y Original Filed De. 20, 1941 miv Ill/nidi( ATTOR//VEK March 13, 1945..v H. TuNlcK RECEP'ITION 0F TIMING MODULATED WAVES Original Filed Deo. 20, 1941 3 Sheets-Sheet 5 fLv ` INVENToR. Harry of the vtulze noise in the l' tube electrically nearest `of the receiver of- Figure is' substantially reduced.

.fed through leads L to a Patentedl Mar. 13,'

yOFFICE l RECEPTION or 'mmm MonULsrEp wsvns muy Tuniek, me, N.

Y., assigner to Radio Corporation oi' America, a corporation of Dela- Original application December 423,763. Divided and this 21, 1942, SeriaiNo. 455,566

20, 1941, Serial No. application August comms.' (c1. aso-2o)- This application isa division of my copending application Serial No. 423,763, led December 20, 1941. My U. S. application Serial No.423,763 is a continuation in part of my U. S. application Serial No. 361,413, filed October 16, 1940, andv now U. S. Patent No. 2,282,101.

The object of my present invention is to provide improved circuits for the reception of angular velocity-or timing modulated waves andk particularly for frequency modulated waves.

In the accompanying drawings, Figure l is a diagram of a receiver, in accordance with my present invention, for receiving angular velocity modulated waves. The arrangement of circuits is such as to secure a substantial reduction in noise.

Figure 2 is a modied form of the system shown in Figure 1, and Figure ment of the apparatus of both Figures 1 and 2. In the receiving system of Figure 1, frequency n modulated waves received upon the antenna RA are fed to a radio frequency amplifier RFA. Most receiver is developed in the first radio frequency amplifying tube of the radio frequency amplier RFA;l that is, in the the antenna; By means 1, this tube noise or hiss Part of the amplified output Aof the radio frequencyamplifier RFA is rectifier R having a large time constant. The output of this recti- -er R is fed through leads L2 to automatically volume control radio frequency amplifier RFA.

Another` portion of the output of the radio fre-` quency ampliiler RFA` is fed through leads LI to a secondrectifier R2 havingv a very small time constant so that theoutput of rectifier R2 pro- 3 isa simpliied arrange-4 tion of limiting,

duces noise voltagesas distinct from desired sig- L nal voltages.

'I'he rst detector DI is fed to a network frequency amplifier -a discriminator DB,

The limiter L6y operates to reducethe amplitude is supplied with locallyv Vgenerated oscillations from the local ,oscillation l generator OG. 'I'he beat frequency or intermeto an audio frequenv.signal carrier. Sincenoise voltages, however, pro

duce waves generally different in frequency than that of, the signal frequency in the limiter, the noise effectively phase modulates the signal output of limiter L6 at such times when the instantaneous position of the noise vector isY not exactly in alignment with the signal vector. It is this phase lmodulation which normally goes through the discriminator and second detector circuits'to produce the undesirablenoise eil'ects in the audio frequency system and this phase modulation noise is produced despite the utilizay balanced detectors and automatic volume control.

By the arrangement shown in Figure 1 the phase modulation component of the noise may be substantially reduced or eliminated. The output of the rectifier-R2 is fed through'manually operated reversing switch RS to a phase modulator PM. The'noise voltage output of rectifier R2 phase modulatesV the waves from the local generator 0G and these phase modulated waves are fed to the ilrst detector. 'Ihe reversing switch RS is throwny to such a position, which will be found by trial, as to introduce in the beat frequency output of the irst detector DI and, there-'-4 fore, in the intermediate frequency amplifier and i limiter, a phase modulation which counteracts the phase modulation produced by the Hunter when the noise components and signal voltages Yare combined therein.

duced by phase modulation within the receiver of Figure 1, the apparatus,D including leads L8,

lter F, reversing switch Rs2, transformer T2 and circuit C, maybe employed. vSince the noise Y output -of the limiter appears as a phase modulation, de-modulation .action by the frequency modulation discriminator D8 and detector D2 will noise voltage in transformer Tl which' rises with increase in frequency of the noise voltage. This noise voltage may be-,balanced out by -feeding the output of rectifier R2 through reversing swith Rs2, its correct position, and circuit C to side of transformer TI. structed vto have a rising it is made so as to lhave an the primary characteristic, namely, output which increases` properly thrown by trial to The lter F is conwith frequency over the noise frequency range.

. In the event that the receiver is provided with a discriminator for phase modulated waves so that the receiver is a phase modulation receiver receiving transmitted phase modulated waves, then, of course, the emphasizing circuit F for the noise voltages may be omitted.

It will be found that the arrangement shown in Figure 1 is especially useful for elimination of QRM or interfering signal which appears Von one vside of the carrier only under certain conditions of reception.

Moreover, as showrrin Figure 2, it is to be noted that the output of rectifier R2 may be used to directly frequency modulate the local oscillation generator, therebyv dispensing with the necessity for the phase modulator PM. Inthis event, however, a filter FF similar to lter F, should be interposed between the rectifier R2 and the frequency modulated local oscillator. Such an arrangement will effectively phase modulate the output of the local oscillator OG.

As a further alternative, as shown in Figure 3, the phase modulator PM, reversing switch RS and filter F, all of .Figure 1, may be omitted and the output of R2 fed either with or without amplification directly into the reversing switch Rs2. This simplified arrangement of Figure 3 will give a general averagingy cancellation of that portion of the noise not eliminated by the limiter.

The frequency swing employed at the transmitter of the system may be of any desirablev value, such as, for example, specified by Hansell in his U. S. Patent 2,179,182. Thus, for example, assuming a transmitter to handle a modulating frequency band of zero to 15,000 cycles, this modulating wave may be used to vary the transmitted frequency plus and minus 15,000 cycles, plus and minus 20,000 cycles, plus and minus 50,000 cycles, plus and minus 100,000 cycles, plus and minus 200,000 cycles, etc. The admittance band of the discriminator, that is to say,

the separation between the resonant peaks of the discriminator circuit, should be made wider than the maximum swing of the received waves.

Having thus described my invention, what I claim is:

1. The method of receiving frequency modulated waves which includes collecting frequency modulated waves, generating local waves, beatingthe local waves with the received waves, deriving from the received waves a voltage representative of noise, phase modulating the locally generated waves with the derived voltage prior to said beating step, converting wave energy de- A rived from the beating step into wavesv of variable amplitude, `detecting,= the waves of variable amplitude and translating the detected waves.

2. The method of treating received angular velocity modulated waves having undesired amplitude modulation components therein, which includes deriving a voltage from said :receivedv waves representative of said amplitude modulation components, generating local waves, phase modulating the local waves with the derived voitiss 3. The method as claimed in claim 2 characterized by the fact that the limited beat waves are converted to waves of varying amplitude, and being further characterized by the fact that the waves of varying amplitude are rectied and utilized to produce the desired modulation of the angular velocity modulated waves.

4. The method of treating received angular velocity modulated waves having therein an undesired amplitude modulation which includes rectifying a portion of the ,waves to produce a voltage representative of the undesired amplitude modulation, angular velocity modulating locally generated waves with the derived voltage, and heterodyning the locally generated modulated waves with another portion of the received waves, and demodulating the resultant beat wave energy so as to produce the desired modulation represented by the angular velocity modulation in the received Waves.

5. Apparatus for receiving angular velocity modulated waves having an undesired'amplitude modulation component therein which includes a circuit for receiving said waves, a rectii'ler for rectifying a portion of said waves so as to derive a copy of the undesired amplitude modulation, a, local generator for generating local heterodyning waves, angular velocity modulating the llocally generated waves with the wave copy derived from the rectifier, a detector to which an other portion of the received waves and the locally generated modulated waves are fed and detected, a limiter for limiting the wave energy output of said detector, and apparatus for utilizing the output of said limiter.

6. Apparatus as claimed in the preceding claim characterized by the fact that circuits are provided for feeding the output of said limiter to a discriminator wherein the limited angular velocity modulated beat energy derived from the detector is converted to waves of varying amplitude, and a second detector for rectifying the waves of varying amplitude derived from said discriminator.

'7. A receiving system for angular velocity modulated waves comprising a circuit for receiving said waves, a rectifier for rectifying a portion of the received waves and for producing a voltage which is a copy of the amplitude modulation component of the received Waves, a local generator, apparatus for phase modulating the wave output energy of said local generator with said voltage, a first detector to which another portion of the received waves and said phase modulated locally generated waves Iare fed for heterodyning, a limiter for limiting the fbeat output energy of said rst detector, and a utilization circuit for utilizing the output of said limiter.

8. Apparatus for receiving angular velocity modulated waves having undesired variable amplitude components therein, which includes a modulating the locally generated waves with the representative voltage, a. detector to which the received waves and the locally generated phase modulated waves are fed for mixing,` a limiter detector, and apparatus 'for utilizing the output .of said limiter.

9. The method `of treatingreceived angular velocity, modulated waves having undesired amplitude variations therein which includes producingfrom said received waves a voltage corresponding to the amplitude variationsin said an- Billar-velocity modulated waves, generating local e -v 2,871,411; l for limiting the beat wave energy output of said I I locally Seneiated waves and said angular 'velocity 'modulated waves. .limiting beat frequency wavefenersy produced by the heterodyning process, and utilizing the limited beat frequency wave

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